Recently, PDPs are gaining attention as displays are getting larger in width and height and getting thinner. A PDP generates an electric discharge in a gas mainly composed of rare gas, particularly, xenon sealed in the panel, thereby to cause a single light body provided in a cell in the panel to emit light. At this time, a part of near-infrared rays and electromagnetic waves generated at plasma discharge in xenon gas atmosphere is radiated to the front surface of the PDP. Such radiation, particularly of a near-infrared ray in the wavelength region from 800 nm to 1100 nm causes problems such as malfunction of cordless telephones or remote control of electrical household appliances, a negative impact on transmission system optical communications, a negative impact on human bodies due to electromagnetic wave, or the like. Accordingly, in order to prevent the above-described problems, a laminated body having a near-infrared ray shielding effect and an electromagnetic shielding effect is provided on the front surface of the PDP.
A near-infrared-absorbing material is added in a laminated body having the above-described near-infrared ray shielding effect. It is desired that the near-infrared-absorbing material adequately transmit light in the visible light range (the wavelength region from approx. 380 nm to 780 nm) so as not to negatively affect luminance of the PDP, and shield a near-infrared ray in the wavelength region from 800 nm to 1100 nm. Conventionally, an organic dye or a metal complex is used as the near-infrared-absorbing material. Use of a filter containing multiple types of the near-infrared-absorbing materials or a multi-layer filter containing various types of near-infrared-absorbing materials in a plurality of layers is proposed.
In such proposals, in the case where an organic compound or a metal complex is contained in a multi-layer filter, a method of coating a substance in which an organic compound or a metal complex is uniformly dispersed in the solvent onto a base material on the PDP surface is commonly used. As a near-infrared absorbent such as an organic compound, a metal complex or the like a diimonium-based compound, an aminium-based compound, a phthalocyanine-based compound, an organic metal complex, a cyanine-based compound, an azo compound, a polymethine-based compound, a quinone-based compound, a diphenylmethane-based compound, a triphenylmethane-based compound are cited. However, such a near-infrared absorbent such as an organic compound, a metal complex or the like is inferior in durability against heat and light. Accordingly, when the organic compound or the metal complex is used as a near-infrared absorbent, it was difficult to maintain near-infrared-absorbing performance for a long period of time.
Further, poor durability of the above-described near-infrared absorbent makes it difficult to provide a layer with a near-infrared ray shielding function in the vicinity of the surface of the visible surface side of the near-infrared-absorbing PDP filter which is susceptible to the influence of an external environment. To address this, in a conventional art, an independent layer is established on the visible surface side in contact with the base material or on the PDP adhesion side, and the layer is caused to have the near-infrared shielding function, whereby durability performance is ensured. However, such structural constraint increases in the number of laminated layers of the near-infrared-absorbing PDP filter, and leads to decreased productivity and increased costs.
Under the above-described circumstance, for example, Patent Document 1 proposes a near-infrared-absorbing PDP filter in which tungsten oxide microparticles or/and a composite tungsten oxide microparticles are dispersed, as an inorganic near-infrared absorbent with excellent weather resistance, in a coating film made of a resin or a metallic oxide provided in or/and on the surface of the base material.
Patent Document 2 proposes an antireflection film, in which a tungsten oxide-based compound is used as a near-infrared absorbent, a hard coat layer containing a cured resin and a near-infrared absorbent and a low refractive-index layer containing a cured resin is sequentially laminated on one of the sides of a base material film. In addition, transmittance of the antireflection film is made to be equal to or less than 30% at least in the entire wavelength region from 850 to 1000 nm. The proposed antireflection film has near-infrared-absorbing performance and anti-reflection performance, has abrasion-resistance, has a simple layer structure, and is manufactured at a low cost and obtained by the wet process method which is particularly preferable for PDP.
In addition, in order to obtain a laminated body having the above-described the electromagnetic shielding function, a method of providing a conductive layer which shields electromagnetic wave on the base material surface is employed. For example, a method of laminating multiple conductive thin films of a metal/a metallic oxide on the base material surface, a method of forming a thin film layer made of metallic foil such as copper and etching the thin film layer into a mesh-like shape, and the like are cited. In the case where the above-described mesh-like metal layer or the above-described metal-containing layer is used, the base material surface on which the mesh is provided is rough. Accordingly, there are some cases where a transparent resin layer is provided to fill the gap thereof, thereby to improve transparency of the optical filter. For example, Patent Document 3 discloses a display. An adhesive agent layer is laminated on a transparent base material, and an electromagnetic shielding adhesive film which is formed by embedding a geometrically-shaped conductive layer onto the adhesive agent layer is adhered to a plastic plate so as to configure an electromagnetic shielding structure body. The electromagnetic shielding adhesive film or the electromagnetic shielding structure body is used for the front surface of the display such as for a CRT, a PDP, a liquid crystal, an EL or the like.
In addition, as the display is getting larger, demand for weight reduction and thinning will be further increased also for PDP. At the same time, improvement of impact resistance of the panel has become an important challenge. Accordingly, for example, Patent Document 4 proposes providing an impact mitigation layer for mitigating an impact from the visual field surface side, in addition to the above-described near-infrared ray shielding layer and the electromagnetic shielding layer.
[Patent Document 1] Japanese Patent Application Laid-Open No-2006-154516
[Patent Document 2] Japanese Patent Application Laid-Open No. 2006-201463
[Patent Document 3] Japanese Patent Application Laid-Open No. 2000-323891
[Patent Document 4] Japanese Patent Application laid-Open No. 2005-023133